This invention relates to alpha-olefin polymerization catalysts, and more particularly, to catalysts comprising an organoaluminum promoter and the reaction product of a magnesium (II) alkoxide, a titanium (IV) alkoxyhalide, and an alkylaluminum halide.
In the low pressure polymerization of alpha-olefins substantial economic benefits can be derived by carrying out the polymerization in the presence of highly active catalysts such that polymeric products are produced in yields high enough to eliminate the need for removal of catalyst residues. To this end catalysts comprising an organoaluminum promoter and a transition metal compound bonded to a support material have been proposed.
One such catalyst, described in U.S. Pat. No. 3,644,318 to Diedrich et al., comprises an organo-aluminum promoter and a solid component prepared by reacting a titanium (IV) halide or alkoxyhalide with a magnesium (II) alkoxide at 0.degree. to 200.degree. C. in an aliphatic, cycloaliphatic, or aromatic diluent. The resulting hydrocarbon insoluble product is then separated from the diluent and washed in a material capable of dissolving any unreacted titanium (IV) compound to remove the same. The washed component then is activated with an organoaluminum promoter at 20.degree. to 150.degree. C. and employed in the polymerization of alpha-olefins. Alternatively, the washed product is treated with an organoaluminum compound at -30.degree. to 100.degree. C. prior to polymerization, and, when the organoaluminum compound employed contains chlorine, the treated product is washed and then activated with a promoter at 20.degree. to 150.degree. C.
While the above-described catalysts exhibit sufficiently high activities to eliminate the need for removal of catalyst residues from polyalpha-olefins produced in the presence thereof, difficulties are encountered in catalyst preparation because a hydrocarbon insoluble solid is formed on reaction of the magnesium (II) alkoxide with the titanium (IV) halides or alkoxyhalides in the presence of aliphatic, cycloaliphatic, or aromatic diluents. Not only are large amounts of inert diluent required to suspend this solid so as to facilitate subsequent preparative steps, such as treatment with an organoaluminum compound at -30.degree. to 100.degree. C. according to Diedrich et al., but also, unless the solid is separated from the diluent and washed, incompletely reacted components and undesirable reaction by-products which are soluble in the diluent will remain in the sysem during subsequent preparative steps.
As can be appreciated from the foregoing, it would be desirable to improve the catalysts of Diedrich et al. in terms of preparative ease and economy while maintaining the desirable polymerization activities thereof. It is an object of this invention to provide such an improved catalyst and a method for the preparation thereof. A further object of the invention is to provide for the polymerization of alpha-olefins in the presence of the invented catalysts. Other objects of the invention will be apparent to persons of skill in the art from the following description and the appended claims.
It has now been found that the objects of this invention can be achieved by reacting a magnesium (II) alkoxide with a titanium (IV) alkoxyhalide under conditions such that a liquid, easily handled reaction product is obtained, and then reacting this liquid with an alkylaluminum compound to form a solid catalyst component. Similar to the catalyst components of Diedrich et al., the invented components can be promoted with an organoaluminum promoter and employed in the polymerization of alpha-olefins to polymers having a relatively broad molecular weight distribution and in sufficiently high yields that separation of catalyst residues from the polymeric product is unnecessary. However, unlike Diedrich et al., wherein a magnesium (II) alkoxide and a titanium (IV) alkoxyhalide are reacted in a hydrocarbon diluent to form a solid product suspended in the diluent, the catalysts of the present invention are prepared in a manner which takes advantage of the solubility of magnesium (II) alkoxides in titanium (IV) alkoxyhalides and the fact that when such compounds are reacted neat, that is, in the absence of a hydrocarbon diluent, a liquid reaction product is formed. As a result, there is no need to use large amounts of hydrocarbon diluent to suspend a solid reaction product so as to facilitate subsequent preparative steps. Moreover, there is no need to wash the neat, liquid reaction product because undesirable reaction by-products can be removed with an inert gas purge.
U.S. Pat. No. 3,901,863, to Berger et al. may be of interest to the present invention in disclosing alpha-olefin polymerization catalysts comprising an organoaluminum promoter and a supported component which may be prepared by reaction of an alkylaluminum halide with the product formed by reaction, in the absence of a diluent, of a magnesium (II) alkoxide with a titanium (IV) compound capable of dissolving the magnesium compound. The invented catalysts are distinguishable from those of Berger et al. because the titanium (IV) alkoxyhalides employed according to this invention are expressly excluded from the titanium (IV) compounds utilized according to Berger et al.